[mythtv-users] New to building computers and MythTV

[Rod Smith]

On Wednesday 21 March 2007 12:29, Jon Sustar wrote:
> > What types of broadcasts do you want to record, HiDef or Standard TV.
>
> Standard TV

If you use tuners that do MPEG-2 (or MPEG-4, but that's rarer) encoding in 
hardware, the CPU and disk space requirements for this will be low compared 
to what you'd need for HD content. You could probably get by with a ~600MHz 
Intel CPU (or AMD equivalent), but ~1GHz would be safer. Most of that CPU 
power would be needed for playback. A faster CPU will be required if you use 
a software encoding (aka framegrabber) card, which feeds an uncompressed 
signal to the CPU, requiring the CPU to do the compression. For that, you 
need ~1GHz per tuner. Given modern CPU speeds, you won't have trouble meeting 
the specs even for a system that uses framegrabbers. Keep in mind, though, 
that MythTV enables you to do things post-recording, such as transcode 
(convert to other resolutions, bitrates, and formats) to save space or to 
move the video to other devices. Some of these operations can be 
CPU-intensive. You can do them even with a wimpy CPU, but these operations 
might take an annoyingly long time. I'd guesstimate that you'd need a ~2GHz 
CPU to transcode MPEG-2 to MPEG-4 in realtime, depending on the specific 
recording and transcoding settings.

>  How many channels will you want to record at the same time?
>
>
> I want to have 2 tuners, so I can record and watch at the same time.

There's a 2-tuner device with hardware MPEG-2 encoding, the Hauppauge PVR-500; 
however, I've seen claims that recent versions of it produce poor picture 
quality, so you might be better off with two separate tuners. For that, 
Hauppauge products (particularly the PVR-150, PVR-250, and PVR-350) are 
popular, but there are other options. You might want to peruse the wiki 
entries of tuners:

http://www.mythtv.org/wiki/index.php/Category:Video_capture_cards
http://www.mythtv.org/wiki/index.php/Video_capture_card

Some card-specific entries bury the very important detail of whether they're 
hardware or software encoders.

> How much TV do you want to store for later viewing?
>
>
> For now, I'd probably get a 500gig HDD, but I would also want enough
> internal drive bays to allow for an additional 2 or 3 HDDS.

This has implications for the form factor for your system. Some people like 
small computers for their Myth boxes, but small cases usually don't have much 
room for hard disk expansion. Similarly, small cases may not have much room 
for video capture cards or may require low-profile cards. If you want a 
compact case, you might still be able to get one but use it with external 
devices. USB capture "cards" and external hard disks are available, but of 
course they'll add to the clutter and that may defeat the purpose of getting 
a small case.

> How many TVs do you want to be able to use Myth on?
>
>
> Most likely one, but would it be difficult to use it on two?

That depends on how. You can do it with switch boxes and wiring, but that 
means you won't be able to watch two shows one two different TVs (which is 
mostly an issue for households with multiple people). Setting up the wiring 
can also be a pain. Alternatively, you could set up one TV with a 
frontend-only system (or split the backend work between them, if that would 
be convenient). This would require two computers and some sort of network 
between them, which could be either wired or wireless. You know the physical 
layout of your TVs and your budget, and are therefore better able to judge 
how tricky it would be to lay out wiring vs. building a separate 
frontend-only system.

> Also, is it necessary to have a frontend and backend system?  Or can it all
> be run on the same box?

It can all be in one box.

FWIW, here are the specs for my frontend/backend system:

Biostar PT880 Pro-A7C motherboard
Intel Celeron-D 347 CPU (3.06GHz)
768MB RAM (512MB would be adequate; I started with 256MB, but it was a bit
    limiting so I added 512MB)
ECS AG200T8-D64 video card (SiS chipset, not the best choice; I recommend
    something based on an nVidia FX5200 or FX6200 instead)
HP DVD+/-RW drive
80GB hard disk (I started small with the intent of upgrading in the future)
Generic case
~400W Antec power supply
Wireless (IR) keyboard/mouse with universal remote programmed to emulate
    the keyboard
Hauppauge PVR-USB2 external USB tuner
AVerMedia AVerTV M150-D PCI MPEG-2 tuner
pcHDTV HD3000 HD/NTSC PCI HD/framebuffer tuner

I think that's it. My system is far from optimal; it's a work in progress and 
a learning experience. If I had to do it again I'd probably use different 
items for most of the components. In particular:

- My motherboard uses a VIA chipset, which has a bad reputation for
  compatibility with the ivtv drivers used by Hauppauage PCI cards, which is
  why I haven't bought one of those cards. I bought it because it's got four
  PCI slots, but knowing what I know now I'd sacrifice a PCI slot for another
  chipset. That said, I've not had any problems that I believe are related to
  that VIA chipset -- but I'm not using a card that uses the ivtv drivers.

- The SiS-based video card chews more CPU time than an nVidia card. I
  originally had an nVidia 4000MX card, but it was causing interference
  with the pcHDTV card, so I bought the SiS in the hopes of working around
  those problems, with only limited success.

- The Hauppauage PVR-USB2 tuner is OK, but MythTV can't set its recording
  bitrate. Apparently this is a matter of their using different APIs. On
  the plus side, it produces the cleanest picture of any of my tuners,
  perhaps because it's external.

- I got the AVerMedia AVerTV M150-D cheap on eBay. It was a gamble that
  didn't pay off, although I can't complain given the low price I paid. When
  it works it's OK, but about 1/3 of the time it records a badly distorted
  audio signal, rendering the recording useless.

- I bought the pcHDTV HD3000 a couple of years ago when the broadcast flag
  seemed likely to darken our doorsteps. I didn't get around to actually
  using it until just a couple of months ago. My opinion is that it's a
  piece of junk, although I realize other people have had better luck with
  this model than I have. It can't get clear QAM (HD cable) reception and
  its NTSC tuner is susceptible to some sort of interference in my main MythTV
  box, yielding audio that's got interference (it sounds like audio from
  another channel is leaking in). I've only got it in the system so that I
  can record content via its composite input.

If I were to do it all again I'd use a motherboard with a non-VIA chipset, get 
a pair of Hauppauge PVR-150 or PVR-250 cards, and use a video card with an 
nVidia FX5200 chipset. Of course, I can't promise you'll have a troublefree 
experience if you do this, but at least you'll avoid the specific problems 
I've had.

-- 
Rod Smith
http://www.rodsbooks.com